TEXAS J. OF SCI. 64(2):73-88 MAY, 2012 (PUBLISHED JUNE 2015) FERAL HOG DAMAGE TO ENDANGERED HOUSTON TOAD (BUFO HOUSTONENSIS) HABITAT IN THE LOST PINES OF TEXAS Donald J. Brown, Melissa C. Jones, Jim Bell, and Michael R.J. Forstner Department of Biology, Texas State University-San Marcos 601 University Drive, San Marcos, TX 78666. Abstract.−Feral hogs (Sus scrofa) are considered a destructive exotic invasive species in the U.S., and their abundance appears to be increasing in the Lost Pines ecoregion of Texas. This is of particular concern due to the status of the Lost Pines as the last remaining stronghold for the federally endangered Houston toad (Bufo [Anaxyrus] houstonensis). We documented short-term impacts of feral hogs to pond perimeters, water quality, and aquatic arthropods at ponds on one of the primary recovery sites for the Houston toad, the Griffith League Ranch in Bastrop County. We also investigated the efficacy of exclosure fencing for eliminating feral hog use of a pond on the adjacent Welsh tract. We found that structural damage to pond perimeters by feral hog wallowing resulted in increased nutrient concentrations and total suspended solids in the ponds, but this damage did not affect aquatic predatory arthropod captures. We found the exclosure fence to be an effective barrier for feral hogs. The ability of feral hogs to rapidly degrade Houston toad breeding habitat warrants consideration of proactive control or deterrent measures, particularly at heavily used breeding ponds. ___________________________________ Domestic hogs (Sus scrofa) were introduced to the United States in 1539, and known feral populations were established in South Carolina in the early 1900’s (Hanson & Karstad 1959). By 1959 feral hogs ranged from North Carolina to east Texas, and by 1998 feral hog populations existed across the entire southern and central U. S. (Hanson & Karstad 1959; Gipson et al. 1998). In addition to a rapidly expanding distribution, hog densities within states continue to increase (Tolleson et al. 1995; Waithman et al. 1999). As of 1995 feral hogs were known to be present in 185 of the 254 counties in Texas, with Texas estimated to house up to 50% of the feral hogs in the United States (Wigley 1995). Feral hogs are one of the most destructive exotic invasive animal species in the U. S., and are considered one of the 100 worst invasive species in the world (Lowe et al. 2000). In addition to negative economic impacts to farmers and ranchers (Wigley 1995; Adams et 74 THE TEXAS JOURNAL OF SCIENCE-VOL. 64, NO. 2, 2012 al. 2005), disturbance through wallowing and rooting can cause habitat degradation for wildlife, especially for species inhabiting wetlands. Doupe et al. (2009) showed that feral hogs degraded freshwater turtle habitat in lagoons in Australia through aquatic macrophyte consumption and wallowing, which decreased clarity, dissolved oxygen levels, and pH in the water column. Kaller & Kelso (2006) found that feral hogs altered invertebrate community composition dynamics and increased fecal coliform counts in a Louisiana watershed. Rooting disturbance to soil, forest litter, and vegetation resulted in declines of red-backed voles (Clethrionomys gapperi) and short-tailed shrews (Blarina brevicauda) in Great Smoky Mountains National Park (Singer et al. 1984), and potentially to declines of southern dusky salamanders (Desmognathus auriculatus) and spotted dusky salamanders (Desmognathus conanti) in Florida (Means & Travis 2007). Further, although feral hogs primarily consume plant matter (Everitt & Alaniz 1980), they also consume both invertebrates and vertebrates (Wilcox & Vuren 2009; Jolley et al. 2010). Thus, small vertebrate taxa with high densities near wetlands (e.g., amphibians) could be particularly vulnerable to feral hog predation, as feral hogs routinely visit wet environments to wallow (Wood & Brenneman 1980). The Lost Pines ecoregion of Texas is a 34,400 ha remnant of pine- dominated forest that was isolated from the East Texas Piney Woods ecoregion during the Pleistocene (Bryant 1977; Al-Rabab’ah & Williams 2004). The Lost Pines is home to a diverse array of wildlife (Taber & Fleenor 2003; White 2003; Rebhorn 2004; Marcum 2005; Ferguson et al. 2008), and it is well known as the last remaining stronghold for the federally endangered Houston toad (Bufo [Anaxyrus] houstonensis; Gottschalk 1970). Until recent years feral hogs were not abundant in the Lost Pines and thus feral hog impacts to Houston toad habitat was not a concern (U.S. Fish and Wildlife Service 1984). However, the abundance of feral hogs in the Lost Pines is considered to be increasing, and consequently their impacts on Houston toad habitat is of growing concern. BROWN, ET AL. 75 The purpose of this study was to document short-term impacts of feral hogs to Houston toad habitat, and to assess how the impacts might affect the Houston toad in the Lost Pines. Because this is a recent problem, there are no data linking feral hog activity to Houston toad population trends. However, it is clear from previously published research that feral hogs pose a major threat to amphibian populations, and this paper seeks to increase awareness of this threat to the Houston toad. METHODS Study Area.−This study was conducted on the 1,948 ha Griffith League Ranch (GLR) and the adjacent 157 ha Welsh tract in Bastrop County, Texas. The majority of documented Houston toads in the wild are located on two properties, the GLR and Bastrop State Park (Swannack et al. 2009), which are separated by a straight-line distance of 2.2 km. The property is underlain by deep sandy soils of the Patilo-Demona-Silstid Association (Baker et al. 1979). The forest overstory is dominated by loblolly pine (Pinus taeda), post oak (Quercus stellata), blackjack oak (Quercus marilandica), and eastern red cedar (Juniperus virginiana). The understory is dominated by yaupon holly (Ilex vomitoria), American beautyberry (Callicarpa americana), and farkleberry (Vaccinium arboreum). The GLR contains 17 ponds, which range from highly ephemeral (n = 2) to permanent (n = 3). We have observed Houston toads at 15 of these ponds since we began monitoring reproduction on the property in 2000, and 11 are known breeding ponds. The Welsh tract contains one semi-permanent and one ephemeral pond. We have documented Houston toads and successful reproduction at the semi- permanent pond. Monitoring efforts on the GLR and the adjacent Welsh property have been extensive since 2000 (Forstner & Ahlbrandt 2003; Jackson et al. 2006; Swannack et al. 2009). In 2001 we observed feral hog wallows at the Houston toad breeding pond on Welsh, with continual 76 THE TEXAS JOURNAL OF SCIENCE-VOL. 64, NO. 2, 2012 hog use apparent in subsequent years. In 2008, a hog exclosure fence was installed at this pond, with the goal of excluding hogs from the pond and 8 ha of surrounding upland habitat. In 2001 we also observed feral hogs in upland habitat on the GLR. However, feral hog wallowing at Houston toad breeding ponds on the GLR did not occur until 2005 (pers. obs.) and remained restricted to a single pond (Pond 11) until 2011. In February and March of 2011 we documented wallows at an additional nine ponds. By April of 2011 substantial structural damage to shorelines had occurred at seven of the ponds. Data Collection.−We monitored Houston toad use of the two ponds on the Welsh tract before and after exclosure fence installation. Houston toad surveys are generally conducted during warm humid nights from January to May of each year. The primary purpose of these surveys is to document male chorusing, but we also visit the ponds to collect data on individual males or females. Following chorusing we inspect the ponds for Houston toad egg strands, and subsequently tadpoles and toadlets. In each year since 2001 we have completed more than 12 audio surveys and 10 daylight surveys for the Welsh ponds, and 20 audio surveys and 10 daylight surveys for the GLR ponds. In addition to monitoring Houston toads on Welsh, we investigated the value of the fence for hog exclusion through monitoring of fence-penetration by feral hogs or other large animals. On the GLR, we assessed feral hog wallow impacts to pond perimeters, aquatic arthropods, and water quality using habitat monitoring data collected prior to and after the presence of hog wallows. We documented structural damage to pond perimeters through photographs. We assessed aquatic arthropod changes using samples collected approximately two months prior to, and one month after, initial detection of hog wallows. We sampled aquatic arthropods at eight ponds using a standard dip net (900 micron netting). At each pond we sampled three points along the perimeter, maintaining approximately even spacing between points, and performed three dip net sweeps per point. We stored samples in BROWN, ET AL. 77 plastic collection tubes containing 95% ethanol, and later identified insects to family and other arthropods to class or order. Because this study was concerned with potential impacts to an amphibian, we were particularly interested in insect families that are known to prey upon larval amphibians (Toledo 2005; Wells 2007). We assessed water quality at all ponds holding water during the study period using water samples collected approximately one week prior to, and one month after, initial detection of hog wallows. We sampled water within 1 m of pond edges using 1 L Nalgene® collection bottles. Within 24 hours of collection we estimated pH using a SympHony 5B70P pH meter, filtered pond water through Gelman A/E glass-fiber filters (1 μm pore size), and preserved water samples with 85% sulfuric acid. We extracted chlorophyll a (Chl a) from filters with acetone, and analyzed Chl a using a Turner Designs Trilogy fluorometer. For quantification of total suspended solids (TSS) in the water column, we dried pre-combusted and pre-weighed filters at 60 °C for 48 to 72 hours, re-weighed them, and combusted the filters at 550 °C for four hours (Heiri et al.